The present invention relates generally to heat extraction devices adapted to be used with wood burning or coal burning stoves and fireplaces. More particularly, the present invention relates to a heat exchange system, including a stove and/or a fireplace insert equipped with the system, for extracting heat from burning fossil fuels for warming an adjacent region.
In the prior art a wide variety of fossil fuel stoves, fireplace inserts, and related devices have been proposed. It is known to recirculate a heat exchange working medium between the fire combustion zone within a fireplace, fireplace insert or wood burning stove etc., and to thereafter extract heat and distribute it within an inhabitable region or volume. Most typical prior art systems employ a tubular heat exchanger device disposed within the fire combustion zone of a stove or fireplace etc., and circulate water between it and a remote heat exchanger for thereafter extracting heat from the second heat exchanger by passing air therethrough. The problem with many prior art devices relates to the high pressure operating points chosen. Moreover, a variety of disadvantageous operational problems occur with typical known prior art systems. For example, closed systems present an obvious danger when safe operating temperatures are exceeded. Closed systems are also particularly vulnerable to the buildup of scale and unwanted residue upon the interior of critical tubular passageways, and they necessitate a great deal of extra maintenance. Moreover, typical closed systems require the use of heavier gauge tubing and fittings in compliance with heating and air conditioning codes and regulations. The latter factor results in increased manufacturing expense as well as increased product weight. For consumers desiring to install a heat exchange system of the type discussed by themselves, reduced weight and operational simplicity are advantageous design goals. Most consumers, for example, simply lack the tools, conpetence and expertise to properly install known high pressure closed heat exchange systems of the type reflected by known prior art.
Another problem with prior art devices known to me includes the "automatic" features of such systems. For example, each system must include some form of water or liquid circulating pump to circulate the working heat exchange fluid between heat exchangers and the fuel combustion zone. I have found that the use of a separate reservoir system, preferably disposed apart from the heat exchanger and the fuel combustion zones, may be particularly advantageous in a low pressure system, while particularly vexatious when used in conjunction with a high pressure system. When electrical circuits fail or when electrical power is interrupted, electrical recirculating pumps will of course stop, and operation of the system must be reliably interrupted. However, as will be appreciated by those skilled in the art, a significant lag time exists between electrical power failure and the resultant drop in system temperature and pressure.
It is therefore advantageous to present a system which will automatically drain the otherwise dangerous remote air/heat exchangers and which will automatically fill the reservoir. Examples of prior art include U.S. Pat. Nos. 1,419,367; 4,206,804; 4,154,210; 4,142,506; 4,340,026; 4,252,104; and 4,344,411. Known relevant foreign prior art patents include French Pat. No. 2,485,697 and U.K. patent application No. 2,044,441.